Also here's a tip: Do NOT double up/triple up on engies. The more you have, the more that Sentry busters show up when the announcer calls it out. Recommend only 1 dedicated engie per team, or get raped by running bombs.

Soldiers are mad useful, I used The Direct Hit, levelled up damage and reload speed, knocked out all the trash so the sentry could focus on the high priority targets.

I play Scout whenever I play MvM. Huge run speed, shotgun (shortstop) good for packs. Most importantly scout picks up money drops in a huge radius and is healed and even overcharged by money when he picks it up. Upgrading run speed, jump distance, damage and clip size makes it a very twitchy high damage class to play.